Hurt my dog

Left pur dog over the weekend and when he was home we noticed a flesh wound on his thigh. We go a hold of the owners and they tried to make it seem like it was an allergy reaction!! Took it to a vet and he confirmed the dog was hurt and you can see the skin sc****d off. This dog is like a child to my mum and she is quite distraught. Please dont take your dog here as they will just make excuses if things go wrong, like we are that naive!!